Idiosyncratic drug-induced liver injury (DILI) is a rare disease that develops independently of drug dose, or route or duration, of administration. Furthermore, idiosyncratic DILI is not a single disease entity, but rather a spectrum of rare diseases with varying clinical, histologic, and laboratory features. The pathogenesis of DILI is not fully understood. Standardization of the DILI nomenclature and methods to assess causality, along with the information provided by the LiverTox website, will harmonize and accelerate DILI research. Studies of new serum biomarkers such as glutamate dehydrogenase, high-mobility group box-1 protein, and microRNA-122 could provide information for use in diagnosis and prognosis, and provide important insights into mechanisms of DILI pathogenesis. Single nucleotide polymorphisms in the HLA region have been associated idiosyncratic hepatotoxicity attributed to flucloxacillin, ximelagatran, lapatanib, and amoxicillin- clavulanate. However, genome-wide association studies of pooled cases have not associated any genetic factors with idiosyncratic DILI. Whole-genome and whole-exome sequencing analyses are underway to study DILI cases attributed to a single medication. Serum proteomic, transcriptome, and metabolome, along with intestinal microbiome, analyses will increase our understanding of the mechanisms of this disorder. Further improvements to in vitro and in vivo test systems should advance our understanding of the causes, risk factors, and mechanisms of idiosyncratic DILI.